Stormwater runoff is characterized by the United States Environmental Protection Agency as one of the greatest remaining sources of water pollution in America. Thus, efforts to implement stormwater quality improvement regulations are accelerating across the United States, compelling municipalities and land developers to maximize the usefulness and effectiveness of stormwater infrastructure as never before.
In urban, suburban, and commercial settings polluted stormwater, also referred to wastewater, is often collected in a catch basin, also referred to as a wastewater basin. In its simplest form, a catch basin functions to intercept surface water flows in order to prevent the accumulation of stormwater in an area where flooding could impede traffic or pedestrians, cause property damage, or otherwise present a nuisance. Stormwater collects in the catch basins, and flows through a network of pipes, sewers, and additional catch basins to an outlet point such as a lake, stream, river, ocean, unpopulated area, or similar location where the wastewater may be dispersed without the threat of flood or property damage. However, catch basins are also often the entry point of pollutants from diffuse sources found in stormwater runoff. For example stormwater runoff may contain pollutants such as hydrocarbons (also referred to as “oil”), bacteria, sediment, trash, organic material such as leaves, grass clippings, particulate, soil, detergents, coolants, grease, fertilizer, paint, and feces. As a result, polluted wastewater is often discharged untreated, directly into lakes, streams, and oceans.
As discussed in U.S. Pat. No. 6,126,817 to Duran et al., which is hereby incorporated by reference, many types of equipment and processes have been suggested in the past for reducing the level of pollutants in wastewater. Many of these systems are based on the principle of differential specific gravity separation. The liquid mixture, which usually is wastewater, flows slowly through an elongated path in a liquid-retaining structure, such as, for example, a catch basin. The matter to be collected is usually oil and floatable debris, both of which accumulate on the surface of the wastewater because they have a specific gravity lower than that of water. Alternatively, as the wastewater flows through the catch basin solids carried by the wastewater accumulate on the bottom of the basin. These solids sink to the bottom of the catch basin because they have a specific gravity greater than water.
U.S. Pat. No. 6,126,817 discloses an outlet hood (or “hood”) for use in a catch basin to reduce the flow of oil and other pollutants into an outlet, also referred to as an outlet pipe, in the catch basin. The hood is useful for capturing trash and floatables, and modest levels of free oils, and sediment. The hood is sealably mounted to the wall of a catch basin over the outlet pipe in the wall of the catch basin. The hood is mounted such that the bottom of the hood extends below the lowest level of the outlet. As wastewater collects in the catch basin heavier pollutants sink and collect on the bottom of the catch basin in the sump, the area below the outlet. Other pollutants having a specific gravity less than water, such floatables and oil, float on the surface of the wastewater.
The bottom of the hood prevents pollutants with a specific gravity lower than water from entering the outlet pipe since the bottom of the hood extends below the static water level of the wastewater that accumulates in the catch basin. As the wastewater level rises in the catch basin, water flows underneath the bottom of the hood, which is below the surface of the water, and into the outlet pipe. Pollutants with a specific gravity lower than water, however, remain on the surface of the wastewater. The wall of the hood acts as a barrier and prevents the oil and other floatables from flowing into the outlet pipe. Periodically, the catch basin is cleaned to remove oil and other floatables that have accumulated therein, as well as sediment that has accumulated in the bottom of the catch basin. In this way the hood provides an inexpensive means of reducing the level of pollution in wastewater.
It is known to manufacture an outlet hood by casting or molding a continuous hood from cast iron or fiberglass. The molded hood can be, at least partially, sealably mounted to the wall of a catch basin over an outlet pipe. In some catch basins the outlet pipe protrudes from the wall of the catch basin some distance. The length of the protrusion from the wall varies in each catch basin. Therefore, it is preferred that a single hood can be used in catch basins having varying outlet pipe configurations.
In reference to FIG. 1, a known outlet hood 10 is shown. The hood 10 is installed to the wall 20 of a catch basin over an outlet pipe 30 in the wall 20 of the catch basin. The outlet pipe 30 is shown with hidden lines and its distal end appears to protrude slightly from the wall 20 of the catch basin.
The bottom 12 of the hood 10, shown in FIG. 1, is open. The top 18 and sides 15, 16 of the hood 10 are sealably mounted to the wall 20 of the catch basin. The front of the hood bulges outwardly from the wall 20 of the catch basin. The installed hood 10 forms a hood compartment defined by the wall 20 of the catch basin and the hood 10. Wastewater that accumulates in the catch basin flows under the bottom barrier 12 of the hood 10 and into the hood compartment where it is drawn into the outlet pipe 30. The static water level in the catch basin, i.e. the water level in the catch basin when the net flow fluid through the basin is zero, is defined by the bottom level of the outlet pipe 32. After the hood is installed the surface of the wastewater consists of two distinct areas: (1) the area of the surface wastewater inside the hood compartment, and (2) the area of the surface wastewater outside the hood compartment.
The front and sides 15, 16 of the hood 10 comprise a hood wall 14 that is curved in the horizontal axis and extends along a vertical axis. In known hood 10 designs the curvature of the hood wall 14 is substantially constant. For example, in a cross section plane defined by the static water level in the catch basin the hood wall 14 is substantially a semicircle with a constant radius. This curved shaped extends along the vertical axis of the hood. Both ends of the semicircle 15, 16 are sealably mounted to the flat catch basin wall 20 thereby defining the distinct area of the surface wastewater inside the hood compartment.
The upper portion or top 17 of the hood 10 comprises a semispherical closure as shown in FIG. 1. In known hoods the semispherical closure, or dome 17, has a constant radius equal to that of the curved hood wall 14. The ends of the semispherical dome 17 are sealably mounted to the wall 20 of the catch basin. The dome 17 may include a vent hole or vent pipe, or, as shown in FIG. 1, may be completely sealed. It is preferred that the semispherical dome 17 is sealably mounted to the wall 20 to prevent oil, pollutants, and other floatables that accumulate on the surface of the wastewater from flowing over a top of the hood wall 14 and into the outlet pipe 30, especially during high flow events, when the level of the wastewater rises in the catch basin.
The hood wall 14 is semicircular in the cross section plane defined by the static water level 32 in the catch basin. This constant curvature allows the hood 10 to fit over an outlet pipe 30 that protrudes from the wall 20 of the catch basin, while at the same time provides clearance for wastewater to flow under the bottom 12 of the hood 10 and into the outlet 30.
A disadvantage of known hoods is that they do not efficiently facilitate precipitation of particulate suspended in the wastewater flowing through the catch basin.
Another disadvantage of known hoods is that they do not increase the distance of the flow path of wastewater flowing through the catch basin system, thereby facilitating precipitation of particulate suspended in the wastewater flowing through the catch basin. The ability of solids to stay suspended in wastewater is a function of the energy in the flow path and the settling velocity of the solid particles. Assuming the characteristics of the particles are constant, the goal is to remove as much energy in the flow path as is feasible, thus allowing for particles to settle and flow to continue as required by a given drainage structure (e.g. stopping flow altogether is optimal in terms of settling, but not in terms of a structure still functioning as a drainage facility). The longer the flow path, the more energy that is dissipated over that path and the more solids that will settle out of the wastewater.
Another disadvantage of known hoods is that they do not create multiple flow paths in a laminar fashion to increase the flow path of more rapidly accumulate on the surface of the wastewater outside the hood compartment. With less surface area outside the hood compartment, oil and other pollutants that accumulate on the surface of the water and are more susceptible to being drawn under the hood and into the outlet pipe, especially as the level of pollutants increases, before they can be emptied from the catch basin by service personnel.
Another disadvantage of known hoods is that their ability to prevent oil and other pollutants from flowing under the bottom of the hood and into the outlet pipe decreases as the ratio of the area of the surface water inside the hood compartment to the area of the surface water outside the hood compartment increases. This problem commonly occurs in catch basins having circular cross section in the horizontal plane.
Another disadvantage of known hoods and hood shapes is that they do not prevent ice from forming on the surface of the wastewater outside the hood compartment and proximate to the bottom of the hood.
Another disadvantage of known hoods is that they are susceptible to structure failure in high flow conditions, especially when used in catch basins having a circular cross section. In catch basins having relatively small cross sections water enters at higher velocities. This high rate of flow exerts direct pressure on the hood. Known hoods are susceptible failure under these conditions because they the side of the hood wall are not perpendicular with the circular wall of the catch basin.
Another disadvantage of known hoods is they are not provided with an apparatus that prevents floatables and other debris inadvertently drawn under the bottom barrier of hood from entering the outlet. wastewater flowing through the catch basin and increase the settling ability of the drainage structure.
Another disadvantage of known hoods is that they do not induce a hydraulic wedge in wastewater that flows into the catch basin, thereby inducing two laminar counter-cyclic eddies, both creating a longer flow path than in known outlet hoods. As wastewater is directed toward the known hood in the catch basin the known hood does not efficiently increase the length of the flow path of the wastewater flowing through the system.
Another disadvantage of known hoods is that they do not induce an increased laminar flow path in wastewater that enters the basin and flows toward the circular front wall of the hood.
Another disadvantage of known hoods is that they are difficult to install in circular catch basins (circular in the horizontal plane), especially in catch basins having a relatively small diameter, because there is insufficient space for personnel to sealably mount the hood to the wall of the catch basin due to the curvature of the front of the hood and the curvature of the catch basin wall.
Another disadvantage of known hoods is that they cannot be used in a catch basin having a relatively small cross sectional area and relatively large outlet pipe.
Another disadvantage of known hoods is that their ability to prevent oil and debris from flowing under the bottom of the hood and into the outlet pipe decreases with a larger hood compartment (i.e. hood wall having a larger constant radius). A larger hood compartment occupies a greater area of the water surface in the catch basin. This in turn reduces the area on the water surface outside the hood compartment causing oil and pollutants to
Another disadvantage of known hoods is that they are increasingly difficult to mold from fiberglass or form from metal or plastic as the size of the hood increases. As the dimensions of the hood increase the molding produces a less consistent shape, thereby increasing production costs, and limiting the strength of the outlet hood.
What is desired therefore is an apparatus for reducing the flow of pollutants such as hydrocarbons, sediment, soil, trash, and floatables into the outlet of a catch basin. Another desire is such an apparatus that can be used in a catch basin that has a circular cross section, and a relatively small diameter. Another desire is an apparatus that extends along an axis, and has a wall shaped to partially sealingly fit around the outlet of an interior wall of a catch basin so as to define at least a partially sealable compartment therewith that is open to the outlet and extends below the outlet so that waste materials floating on said water mixture outside of the compartment are prevented from entering said outlet, wherein the wall forms a prow in a cross section plane being defined by a static water level in said catch basin.